Fig. 1. Schematic illustration of the monochromatic ratiometric imaging for quantifying extracellular and intracellular distribution of nanoparticles in living mice.

When accumulating at tumor tissues after intravenous injection, a part of MRINs are endocytosed into cells, then the Cy5 signals of intracellular nanoparticles are activated by the acidic pH of endosome. While the Cy5 signals of extracellular nanoparticles still keep ‘OFF’ state, which could be subsequently activated by 808 nm irradiation-induced Cy7.5 photobleaching. Harnessing MRIN nanotechnology, we can accurately quantify the intracellular and total (intracellular + extracellular) exposure of nanoparticles in tumor sites, thereby quantify the extracellular exposure of nanoparticles in tumor mass.